Morphometric and chronological behavior of 2.45 GHz microwave ablation zones for colorectal cancer metastases and hepatocellular carcinoma in the liver: preliminary report

Abstract

Background: Percutaneous microwave ablation (MWA) is increasingly utilized in the treatment of primary and secondary hepatic malignancy. As an in-situ treatment appreciation of any signs of recurrence is critical for improving long-term oncological outcomes. Volumetry has been recognized as having advantages over orthogonal measurements in the response assessment of malignant lesions. Our study set out to look at the normal involution of an ablation zone (AZ) both volumetrically and morphologically to see if this information might aid the detection of local tumor progression.

Methods: Cases were identified retrospectively from our database of liver MWA. We identified 34 AZs in total, 18 AZs in 16 hepatocellular carcinoma (HCC) patients with cirrhosis on imaging grounds and 13 AZs in patients with metastatic colorectal cancer. How these AZs developed over time was analyzed both morphologically and quantitatively using Siemens Syngo Via post-processing software. We used the software to produce volume measurements and short axis orthogonal measurements. A baseline measurement was taken on the first <30 day post-ablation scan and the chronological changes were then plotted.

Results: We saw differences between the cirrhotic and non-cirrhotic patients both in terms of morphological and volumetric changes. 12/13 non-cirrhotic AZs had a volume of <50% of the baseline scan within the first year. The cirrhotic patients were less predictable, but 14/18 still shrunk to less than 50% of baseline volume in the first year. Orthogonal measurements were less useful in both groups. Qualitatively, there was initially a slightly less well-defined border to the AZ in the first 3 months, which became better defined over time and certainly over the first year of AZ involution.

Conclusion: Volumetric analysis is a useful adjunct to conventional measurements and qualitative analysis of AZs. This can be reassuring when orthogonal measurements are static or difficult to interpret. Our preliminary data suggest that the normal pattern in a non-cirrhotic liver is that the AZ volume should drop below 50% of baseline at 1 year. Volumes in cirrhotic livers are less predictable, but the majority will still follow a similar pattern. Future studies could evaluate if failure to follow these patterns correlates with local tumor progression.

Keywords: Colorectal cancer metastasis ablation; Hepatocellular carcinoma abation; Involution; Liver ablation; Microwave ablation zones; Volumetric analysis.